38 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CIRC 42 
The Control of Peach Diseases—Peach diseases are usually con- 
trolled in one or more of the following ways: (1) by planting a variety 
that is immune or resistant to the disease; (2) by planting a variety 
only in the locality where the disease is not serious; and (3) by the 
use of direct control measures, such as spraying or disinfection.?® The 
quarantine service is a means of preventing the introduction and 
spread of new diseases and insects within the state 
Fig. 10.—Peach roots of young tree infected with erown call, 
Crown Gall, Bacterium tumefaciens S. & T.—The bacterium caus 
ing crown gall or root knot is found in many soils. Swellings or tumor- 
like enlargements are formed on the crown and the main roots and 
sometimes on above ground parts of the tree (fig. 10). A tree affected 
by this disease shows a loss of vigor, and may eventually die, The 
trouble may be lessened by inspecting and rejecting diseased nursery 
trees, and by care in cultivation so as not to wound the trees. Examine 
the erown and main roots of stunted trees for evidences of the disease 
20 Horne, W. T., E. O. Essig and W. B. Herms. Plant disease and pest control. 
California Agr. Exp. Sta. Cir. 265:1-182. 1927.